The present invention relates to devices for controlling a starter for a motor vehicle.
Traditionally, the power supply to the electric motor of a starter is controlled by an electromagnetic power contact (coil relay) which is actuated as a function of the state of the vehicle""s contact switch, either directly or via a management electronic circuit which may or may not be incorporated in the starter.
When the starter is deactivated after the thermal motor has started, the armature does not return to a stationary position immediately. The armature""s rotation speed is at a maximum at the moment of deactivation, and it then falls gradually over time. The time taken for such slowing depends on the maximum speed, on the inertia of the armature and on frictional losses.
For conventional starters, the time taken to stop may amount to several seconds, during which the starter emits noise at different frequencies. In general, this noise is irritating because it is easily perceptible inside the vehicle passenger compartment.
To reduce this irritation, attempts are being made to reduce the slowing time so that it is short enough to prevent the structure of the starter and its components from beginning to resonate.
To this end, proposals have already been made to brake the armature of the starter""s electric motor mechanically using a friction disk arranged between said armature and a stator bearing.
However, such mechanical braking has the drawback of being permanent and, in particular, of being present throughout the time in which the starter is operating. This considerably reduces the efficiency of the starter.
Furthermore, such braking is not reliable over time, and its effectiveness changes as the frictional parts become worn.
To overcome these drawbacks, proposals have also been made for starter structures in which an auxiliary mechanical contact electrically grounds the power supply terminal of the starter""s motor as soon as the starter""s power contact returns to its open position.
One aim of the invention is to propose a simpler device which enables the electric motor of a starter for a motor vehicle to be braked reliably over time and does not impair the efficiency of said starter.
In its patent application FR 98-11,550, the applicant has recently proposed a device for controlling the power supply to the electric motor of a starter in which the power contact is not a moving contact, but is a static relay in the form of a controllable electronic component, such as a power transistor.
Another aim of the invention is to propose a solution for braking the electric motor of a starter which may be used in the case where said electric motor is controlled by such a static relay.
To this end, the invention proposes a device for controlling the power supply to the electric motor of a starter for a vehicle, particularly a motor vehicle, having a power switch connected in series with said electric motor, means for controlling said power switch, and an auxiliary switch which shorts said electric motor when the power switch is opened, characterized in that said auxiliary switch is a static electronic component.
This solution enables the slowing of the armature to be governed using a very simple structure.
It is additionally compatible with the use of a static electronic power component to produce the starter""s power switch.
Moreover, the device proposed by the invention is advantageously supplemented by the various features below, taken on their own or in all their possible combinations:
a static electronic component is a transistor;
the auxiliary switch is controlled by a microcontroller which manages the control of the power supply to the electric motor;
the static electronic component forming the switch is connected in series with a resistor;
the static electronic component forming the auxiliary switch is controlled by a pulse-width-modulated pulsed signal;
the static electronic component forming the switch is controlled in open loop mode;
the static electronic component forming the switch is controlled as a function of the strength of the current passing through it;
the device has shunt-type means which are connected to an analog/digital input on the microcontroller and transmit to said input a voltage which is proportional to the strength of the current passing through the static electronic component forming the switch;
the device has means for turning on the auxiliary switch when the contact switch of the starter and the power contact (K) are open, and for turning it off otherwise.
The invention also relates to a starter for a vehicle, in particular a motor vehicle, having an electric motor, a gearwheel driven by said motor, means for moving said gearwheel from a position of rest to a position in which it engages with a ring gear on the thermal motor, and also to a device of the aforementioned type for controlling the power supply to its electric motor.